Sequenced Antenna Array For Determining Where Gaming Chips With Embedded RFID Tags Are Located On A Blackjack, Poker Or Other Gaming Table &amp; For Myriad Other RFID Applications

ABSTRACT

An improved antenna system, method and apparatus for interrogating and locating RFID (Radio Frequency Identification) tags and other RF (Radio Frequency) devices, and various applications therefore and thereof, are disclosed. One embodiment is for reading and locating the physical position of RFID tags (such as is made by Phillips, Siemens&#39;s Infineon and Texas Instrument) that may be embedded in gaming chips (RFID gaming chips, such as is made by Gaming Partners International Corp.) used in a casino, TV or movie studio or elsewhere for wagering at table games and other gambling games including Blackjack, Poker, Craps, Baccarat and Roulette, but the invention may be used for various other RFID applications.

This application claims the benefit of U.S. provisional patentapplication No. 60/707,375 titled “Sequenced Antenna Array ForDetermining Where Gaming Chips With Embedded RFID Tags Are Located On ABlackjack, Poker Or Other Gaming Table & For Myriad Other RFIDApplications” filed Aug. 10, 2005, which is incorporated herein byreference in its entirety.

The following U.S. patents and Other References listed are incorporatedin this application by reference: Pat. No. InventorTitle 6,903,656 LeeRFID reader with multiple antenna selection and automated antennamatching 6,750,769 Smith Method and apparatus for using RFID tags todetermine the position of an object 6,712,696 Soltys et al. Method andapparatus for monitoring casinos and gaming 6,663,490 Soltys et al.Method and apparatus for monitoring casinos and gaming 6,661,335 SealSystem and method for locating radio frequency identification tags6,579,181 Soltys et al. Method and apparatus for monitoring casinos andgaming 6,579,180 Soltys et al. Method and apparatus for monitoringcasinos and gaming 6,535,175 Brady et al. Adjustable length antennasystem for RF transponders 6,530,836 Soltys et al. Method and apparatusfor monitoring casinos and gaming 6,527,271 Soltys et al. Method andapparatus for monitoring casinos and gaming 6,520,857 Soltys et al.Method and apparatus for monitoring casinos and gaming 6,517,436 Soltyset al. Method and apparatus for monitoring casinos and 6,514,140 StorchSystem for machine reading and processing information from gaming chips6,509,836 Ingram Smart reflection antenna system and method 6,396,438Seal System and method for locating radio frequency identification tagsusing three-phase antenna 6,392,544 Collins et al. Method and apparatusfor selectively activating radio frequency identification tags that arein close proximity 6,362,737 Rodgers et al. Object Identification systemwith adaptive transceivers and methods of operation 6,313,871 SchubertApparatus and method for monitoring gambling chips 6,267,671 Hogan Gametable player comp rating system and method therefor 6,234,900 CumbersPlayer tracking and identification system 6,142,876 Cumbers Playertracking and identification system 6,094,509 Zheng, et al. Method andapparatus for decoding two- dimensional symbols in the spatial domain5,809,482 Strisower System for the tracking and management oftransactions in a pit area of a gaming establishment 5,781,647 Fishbineet al. Gambling chip recognition system 5,735,742 French Gaming tabletracking system and method 5,651,548 French et al. Gaming chips withelectronic circuits scanned by antennas in gaming chip placement areasfor tracking the movement of gaming chips within a casino apparatus andmethod 5,566,245 Zheng, et al. The performance of a printer or animaging system using transform-based quality measures 5,283,422 Storchet al. Information transfer and use, particularly with respect tocounterfeit detection 4,896,029 Chandler, et al. Polygonal informationencoding article, process and system 4,874,936 Chandler, et al.Hexagonal, information encoding article, process and system 4,814,589Storch et al. Information transfer and use, particularly with respect toobjects such as gambling chips 4,797,682 Klimczak Deterministic thinnedaperture phased antenna array 4,531,187 Uhland Game monitoring apparatus4,026,309 Howard Chip structure 3,983,646 Howard Chip structure3,926,291 Burke et al. Coded Token and Acceptor 3,766,452 Burpee et al.Instrumented Token

OTHER REFERENCES

-   -   “Item-Level Visibility in the Pharmaceutical Supply Chain: A        Comparison of HF and UHF RFID Technologies”    -   A white paper from Philips Semiconductors, TAGSYS and Texas        Instruments Inc. Published July 2004    -   “RFID Shelf Antennas” by Bob Scher, CEO, Dynasys Technologies,        Inc.    -   Copyright© 2004 Dynasys Technologies, Inc., 800 Belleair Rd.,        Clearwater, Fla.

According to an embodiment of the invention, a system is provided toidentify gaming chips bet on a casino gaming table. The system comprisesa plurality of gaming chips each comprising an RFID device whichcomprises a unique RFID number and a peripheral bar code representing adenomination and a casino gaming table comprising player bettingpositions for betting one or more of the plurality of chips. The systemincludes means associated with at least one given position for readingoptical bar codes of any chip of the plurality of chips placed in thegiven position and providing the number thereof. The system alsoincludes means associated with the given position comprising two or moreantennas for transmitting interrogation signals in an excitationsequence to respective RFID devices of any chip of the plurality ofchips placed in the given position and for receiving a signal sequencefrom the respective RFID devices in response to the interrogationsequence, and means for processing a received signal sequence toidentify respective unique RFID numbers and providing the number thereofand for comparing the number of chips provided by the means forprocessing and the number provided by the means for reading optical barcodes.

According to some embodiments, the two or more antennas comprises atleast one other antenna with different a coverage pattern than the twoor more antennas. According to some embodiments, the one other antennais positioned between the two or more antennas.

According to some embodiments, the means for transmitting interrogationsignals in an excitation sequence does not provide for signals fromevery antenna associated with the at least one given position.

According to some embodiments, the means for processing employs acomputer algorithm to determine which antennas are excited and theexcitation sequence thereof.

The example that follows describes a casino Blackjack table with playingpositions for seven players. Each player has an assigned “bettingposition” on the table to wager his RFID enabled gaming chips. If aplayer wins a hand, the dealer places his winnings in his bettingposition. Various known means may be employed to associate an individualplayer's identity with one or more betting positions on a Blackjacktable before, during or after a player's play session.

FIG. 1 shows three stacks of chips, C1, C2 and C3, each stack with 21chips sitting in adjacent betting areas on a Blackjack table top T1.Below each of the three table top betting areas is an antenna depictedas a “target/sight” in FIG. 1 and labeled A1, A2 and A3. The threestacks are in respective juxtaposed betting areas. Each chip isperipherally bar coded with its denomination value using, for example,coding such as described in Pat. No. 6,514,140. Each chip also has anembedded RFID tag with information comprising: (at least) a unique RFIDnumber, and various other information. The RFID tag may or may not haveread/write capability.

One or more chips with RFID tags sufficiently proximal to antenna A1,for example, may be interrogated by antenna A1 via a transmission fromA1, and the tag(s) may transmit a respond to the interrogation with maybe received by antenna A1. This is a typical transmit interrogation andresponse cycle, and it is well known in the art.

In an embodiment of the invention, two adjacent antennas are operated atdifferent times because otherwise one antenna may activate a responsefrom a chip over the other antenna. For example, referring to FIG. 1, ifantennas A1 and A2 were activated together, A1 may receive an unwantedresponse from a chip in the stack of chips C2 above A2 if A2 activatesat the same time as A1, and visa versa.

Optically reading the chips bar codes, as described for example in U.S.Pat. No. 6,514,140, can be used in conjunction with reading the RF tags,for reasons including the ability to assist in accurately locating andreading chips. For example, optical readings could identify the numberof chips and of what denomination in a particular betting area so thatthe RF reading can be compared to the optical reading results. Ifdiscrepancies were to exist between the optical and RF readings, theycould be resolved with further processing.

The following describes one possible example of how optical and RFIDreading could work together to provide more accurate, corrected resultsin the event of, for example, a spurious RFID reading: If the opticalsystem were to see 10 chips of the $25 denomination in a given bettingposition, but the RF readings included 11 $25 chip responses that appearto be from that betting position, the unique RFID numbers of the 11chips could be compared to the left and right adjacent betting positionRF readings in order to determine which one of the 11 chips' unique RFIDnumbers was also found in an adjacent position, so that its presencecould be automatically removed from the RF reading tally that containedthe 11 RF chips' responses. Or, in some cases if chip trackingprovisions were being utilized, the tracking history of one of the 11chips might reveal that it currently belongs to another player atanother playing station. Thus, the discrepancy revealed by thecombination use of RFID and optical readings could be resolvedaccurately.

Comparison of optical readings with RFID readings may be helpful oruseful to: (i) detect the location of particular chips in order to (ii)help identify faulty or damaged RF or optically coded chips, (iii)detect counterfeit chips, (iv) detect stolen chips, and (v) detect chipsbeing tracked for a variety of management or official (e.g., government)purposes, so that such chips can be to removed, replaced, repaired ordeal with it as appropriate or according to a particular casino or otherpolicy.

As has been mentioned in various prior art, casino management would liketo bring the player evaluation/tracking abilities long used for slotmachines to the gaming table. Using the present invention, casinos canmore accurately track table play, without requiring more effort on thepart of dealers and other casino personnel, and without changing the waytable games are played. Management can give more rewarding “comps” forplayers that provide more profit to the casino, as well more accurate,lower comps for players that get or have been getting more than theydeserve. Improved, more accurate evaluation of players' skill, detectionof players who employ suspect strategies, and more accurate accountingof employee efficiency and performance, as well as tighter security fortable game operations is also possible.

In a game like Craps, for example, players do not have assigned bettingposition like on a Blackjack table. In Craps, different positions on thetable relate to different bets which are indicated by the markings onthe table covering. Different bets have different payout odds associatedwith them. For example, the “2” (snake eyes) and 12 (box cars) betslocated in the “Field” pay double in the event a player placed such abet and wins.

The RFID antenna array system described herein could be used to gleaninformation about Craps table bets; for example, it could detect when a“2” Field bet is made, and, using known means to read the dice on thenext roll, automatically determine if that “2” bet won or lost. If itwon, it could then interrogate additional chip(s) placed as payout bythe dealer next to this winning “2” chip(s) that had been bet, and (i)provide information as to whether or not the correct amount has beenpaid, (ii) associate the unique RFID number of the chip(s) in the payoutwith the unique RFID number of the chip(s) wagered. If the casino systemwere tracking the RFID numbers of chips in the possession of specificplayers, the chip(s) won on the “2” bet in this example could beassociated with the specific player who made this winning “2” wager.

According to an embodiment of the invention, a system and method areprovided using an antenna array for interrogating and locating RFID tagscomprising more than one antenna means to transmit a series or set ofsignals, e.g., in a programmed sequence, the antenna means being able toreceive signal responses from sufficiently proximal RFID tags, andassociated program means to determine tag location from informationderived (i) from responses to specific antennas and/or (ii) fromnon-responses to other specific antennas. A heuristic program to improvesystem efficiency may be employed. One embodiment described by way ofexample involves reading and locating gaming chips.

One purpose of the improved antenna invention described herein is toidentify which RFID chips are bet and/or won at each individual(localized) player betting position so that information may beassociated with the particular player making the bet. A “positionlocation strategy” will be referred to below in describing how thelocations of individual chips are associated with betting positions onthe table. (Well known means are used to associate specific bettingposition(s) with specific players.)

Referring to FIG. 6 depicting a single antenna, of the type describedbelow, and to FIG. 6A depicting an antenna array comprised of multiplesingle antennas, what follows is an example of how this purpose may beaccomplished: Place a plurality of strategically positioned low power,directional (high gain, such as but not limited to, coil or patch type)antennas in, on, under or associated with a table surface, with eachantennas' emitted pattern center axis all projecting parallel to eachother and up in the air orthogonal (or reasonably orthogonal, i.e., atan angle that will work with the invention) to the top of a blackjack orother gaming table surface. The use of a high gain antenna provides fora more narrowly focused and subsequently more controlled directionalpattern. The use of low power (made possible due to the very shortoperating/detection distances) provides for minimal reflected energywhich could indirectly cause secondary reflections from exciting (chiptag) antennas of non-interest. The antennas would need to be placedbelow the top playing surface of the table only far enough (the distancecould be zero) such that the emitted pattern would be developed(cross-sectionally) enough by the time it reaches the table surface toprovide for a fairly cross-sectionally uniform pattern from the tablesurface to somewhere about 4-5 inches above so as to read a stack ofabout 20, more or less, gaming chips. The use of a narrower or not fullydeveloped pattern however could provide additional assistance inproviding a higher resolution positioning accuracy at the table surface,but may require additional processing in associating tags to stacksbecause the lower chip(s) in the stacks may not be seen by as manyantennas.

The table surface material properties would also need to not vary withtime (holding moisture, etc.), and be fairly transparent (loss-less) tothe RF energy at the frequencies of interest (in this embodiment, welikely will be projecting and receiving through the table surface andone or more possible table coverings) so as not to distort the patternsor attenuate any transmitted/received energy (or to minimize thedistortion of the patterns or attenuation of any transmitted/receivedenergy). It is also possible to make the antenna structure part of thesurface of the table. For example, the antenna may be embedded in thetable surface or the covering, and a felt or some other gaming table topcovering may or may not be used to cover the antenna and the table top.The goal would be to have the emitted patterns as tight around the waistto provide for a higher degree of x-y positioning accuracy, with the zaxis being the center of the emitted pattern axis (orthogonal, orreasonably orthogonal, to the table surface). A HF (high frequency)system (for example, 13.56 MHz) may be preferred because these systemstend to work with magnetic fields (near field), rather than electricfields. They may be easier to create in defined areas (like positions ona table), and reading multiple tags may be somewhat easier. Also, waterand other similar materials do not present as much of an interferenceproblem. Higher frequency tags (for example, 916 MHz-5.8 GHz) could alsobe used, but might result in a more challenging and higher cost solutionwith little if any performance advantage.

In this Blackjack embodiment, the position location strategy would be toenable one antenna at a time within a given zone and de-tune andde-activate (turn-off) all remaining antennas in that zone. The size ofthe zone would be such that tag detection activities in the frequenciesof interest in one zone using the antenna structure of choice would notimpact synchronized or unsynchronized activities in another adjacentzone. If the total working area is small you might only have one zone,where as larger areas could provide for multiple (non-interfering)zones. This scalable approach also allows for covering larger positiondetection areas while minimizing the impact on position detection timesdue to the parallel operation.

Zone size/area allows for parallel operation on a table surface; zonesize provides for simultaneous activation of multiple antennas in agiven excitation sequence and provides enough spatial separation so asto prevent interference from a neighboring zone.

In FIG. 7 two antenna zones, each zone with 9 antennas, are shown; Zone1 and Zone 2. FIG. 7 shows the definition of zone matrix size based onthe worst case cross-sectional emitted antenna element pattern as viewedlooking into the table surface (−z axis). With sufficient spatialseparation, an antenna operating in one zone would not impact theoperation of an antenna operating in a neighboring zone. As shown inFIG. 7A, the worst case emitted pattern diameter or area of influencefrom an active antenna “d” defines the minimal zone separation or pitch“d” of active antennas operating in adjacent zones.

In FIG. 8A four zones are shown, i.e., zones 1 to 4. Each zone has nineantennas. Each zone forms a quadrant of a square; the whole square asdepicted has a total of 36 antennas. The lower left antenna in each ofthe four zone-quadrants can be excited simultaneously in thisembodiment. This is because the effective excitation/coverage area ofeach antenna, which is depicted by the circle shown around each lowerleft antenna in each quadrant, does not reach or overlap into any otheractive-at-the-same-time antenna area. Therefore, these four antennascannot interfere with each other even if all four are activatedsimultaneously. This exemplifies how system recognition/throughputefficiency can be improved by simultaneous operation of non-interferingantennas in adjacent structured zones: Instead of requiring enough timefor 36 complete antenna activation cycles, only nine such simultaneouscycles would be required to poll all 36 antennas.

Related FIG. 8B shows activation of four antennas; each antenna at thispoint in the activation sequence is located in the center of itsrespective zone. These four centrally located antennas can be activatedsimultaneously in some sequence (for example) after those in FIG. 8A.

Also related FIG. 8C shows activation of four antennas, possibly next inthe activation sequence. These antennas are located in the upper rightcorner of their respective zone. These four antennas can be activatedsimultaneously (for example) after those in FIG. 8B.

It should be noted however, that the antenna excitation sequence neednot be consecutive, nor even include every antenna. In some embodimentsonly enough antennas need be excited to provide sufficient results toprovide the information being sought. It is possible to employ aheuristic computer algorithm to dynamically determine the excitationsequence to improve system efficiency.

It is important to note that only one antenna per zone may be active atany given time with all non-selected (and non-active) antennas in thearray for that zone being de-tuned and de-activated (turned-off) so asto not interfere with the enabled antenna and associated tags withinrange (i.e., tags that respond to the one enabled antenna in a givenzone). An algorithm as described below may be used for determining thesequence (and position) for enabling antennas. Preferably, the algorithmwould account for the physical proximity of any excited antennas inadjacent zones to optimize (minimize) zone size.

FIG. 9 shows nine antennas arranged 3×3 that make up one zone. Thefollowing example will describe how the physical location of one RFIDtag positioned within the zone of this example could be determined. Thisone tag itself in this example is not shown per se, but for the purposeof this example, this one not-shown tag will be referred to as “thatchedtag”, and the top center antenna will be referred to as the “thatchedtag antenna”. The thatching being referred to as shown in FIG. 9 is madeup of vertical and horizontal lines (similar to lines on grid paper).(Of course, the location of more than one tagged casino chip in a stackof chips above the thatched tag antenna is possible.)

If antennas numbered 1, 2 and 3 in FIG. 9 each in turn had a responsefrom thatched tag, and the un-numbered antenna positioned directly belowantenna position number 1 did not get a response from thatched tag,thatched tag must therefore be located above the thatched tag antenna—itcould not be above any other antenna location in this example andrespond, and not respond, to the antennas as described. I.e., taglocation information may be derived from (i) responses to specificantennas and from (ii) non-responses to other specific antennas, as thisexample demonstrates.

The technique for determining tag position (i.e., the location of tags)on the table surface may also be described as follows: Antenna 1 in agiven zone would be enabled (excited), and the group (“group 1”) of tagsthat subsequently respond to that first antenna would automatically berecorded and associated with antenna 1 activation. Adjacent antenna 2next in the excitation sequence (in the same zone) would be enabled andthe subsequent responding group of tags recorded and associated withantenna 2.

Antenna 2's group (“group 2”) would be compared by an automatic programagainst group 1 (those group 1 tags that responded to antenna 1). Theresult of the comparison of the two groups would reveal which tags werein group 1 but not in group 2, and visa versa. Tags that are new to, oradded to, group 2 are closer to the second antenna in a direction movingaway from antenna 1, and tags that responded in group 1 but did notrespond in group 2 are closer to antenna 1 in a direction moving awayfrom antenna 2. By using this technique of tags adding to adjacentantenna's groups, and tags dropping out relative to inquiries fromadjacent antenna's positions, the physical location of tags present onthe table surface can be determined.

It is also understood that the antenna arrays only be placed in andaround areas where chips would be present on the table surface, thusoptimizing the sequence cycle speed required for position detection. Forexample, a Blackjack game has limited and more controlled chip placementareas on the table surface and would need a less complicated antennaarray and excitation sequence than a table game with more positions, orwith no specifically-assigned-to-one-player gaming positions, such asCraps. For example, antennas for a Blackjack table may be placed along aline (for example, a straight or a curved line).

In another embodiment, it is possible to include different types ofdirectional antenna coverage patterns within the matrix (low gain suchas shown in FIG. 10A, and high gain such as shown in FIG. 10B) such thata centrally located/zone centered lower gain (broader pattern, andperhaps higher power emitted patterns) surrounded by higher gaindirectional (as shown in FIG. 10C) allow for quick determination of thepresence of tags in a macro sense within an entire zone such that zoneareas not receiving a response to a macro inquiry do not warrant furtherhigher resolution inquiries using the surrounding higher gain antennas.It is also possible to dynamically re-define zone and activationboundaries based on the macro presence response to ultimately speed tagdetection/location cycle times.

FIG. 2 is similar to FIG. 1 but an additional antenna is shown beneathtable top T2 in-between each chip stack's (C4, C5 and C6) betting area:from left to right the antennas shown in FIG. 2 are labeled A4, A5, A6,A7, A8, A9 and A10.

FIG. 3 is similar to FIG. 1 and FIG. 2 but two additional antennas areshown beneath table top T3 in-between each chip stack's (C7, C8 and C9)betting area: from left to right the antennas shown in FIG. 3 arelabeled A11, A12, A13, A14, A15, A16, A17, A18, A19, A20, A21, A22 andA23.

FIG. 4 shows 39 antennas arranged in an X-Y grid. Three rows of antennasare shown, Y1, Y2 and Y3, and thirteen columns of antennas are shown inFIG. 4: from left to right the antennas' 13 columns are labeled X1, X2,X3, X4, X5, X6, X7, X8, X9, X10, X11, X12 and X13. The antenna arrayshown in FIG. 4 could be used on a Blackjack table to provide the depthof three rows of RF readings for the betting positions in order toprovide more data so that the betting position location of the RF taggedgaming chips can more accurately be determined.

FIG. 5 shows 169 antennas arranged in an X-Y grid. Thirteen rows ofantennas are shown, from bottom to top Y1 to Y13, and thirteen columnsof antennas are shown in FIG. 5: from left to right the antennas' 13columns are labeled X1 to X13. The antenna array shown in FIG. 5 couldbe used on a Craps table (or a portion of a Craps table) to provide thedepth of thirteen rows and thirteen columns of RF readings for the betsplaced by any one of several players so that the position location ofthe RF tagged gaming chips can be determined.

Antennas for a Craps table may, for example, be placed according to x-ygrid lines (like the “grid line” arrangement that makes for the 64 boxeson a chessboard, or, not shown, arranged like the elements of UPS's 2Dbar codes including Maxicode; see, for example, U.S. Pat. Nos.6,094,509, 4,896,029 and 4,874,936, which describes symbols constructed,for example, as a matrix of hexagonal information-encoding elementsarranged in a square) and may contain a number of antennas sufficient toaccurately determine the location of wagered chips and so that, forexample, the correct wager information and information about winningbets can automatically be determined and the amount paid can becorrelated to the automatic determination when the chip(s)-in-paymentare placed in proximity to a winning bet.

What follows is an operating example of one possible embodiment using aBlackjack table by way of example. However, the principles explained inthis exemplar embodiment may be applied by those skilled in the art toutilize more antennas in appropriate arrays as shown, for example, inthe Figs.

Antennas may be positioned adjacent to each other at suitablepredetermined intervals along a line under a Blackjack table surface. Asequence of their activation and operation in order to determine onwhich betting positions individual RFID gaming chips are locatedfollows:

If chips “a” to “m” respond when a first antenna is activated, and chips“a” to “d” and “h” to “p” respond when a second antenna is activated, itthen can be determined that chips “e,” “f,” and “g” are closer to thefirst antenna and in a direction further from the second antenna, andchips “n,” “o,” and “p” are further from the first antenna and closer tothe second antenna. In Table 1, chips responding in turn to the firstand second antennas are in bold type and underlined. TABLE 1 Firstantenna: a b c d e f g h i j k l m n o p q r s t u v w x y z Secondantenna: a b c d e f g h i j k l m n o p q r s t u v w x y z

By continuing this example for all antennas in the array's pattern, therelative positions of all responding chips could be determined.

Another way of how to describe how to determine a chips physicalposition (micro sense vs. actual macro operational mode) using theexclusion algorithm could also be described as follows. To find theposition of a single chip, find the edges of that chips' responsepattern to other surrounding antenna patterns; basically, at whatantenna positions did that chip fail to be recognized?

In other words and as mentioned above, a given tag's locationinformation may be gleaned from (i) what antennas a tag responds to, andfrom (ii) what antennas a tag does not respond to.

If you then connect the dots of the points on the inside the respectiveantennas coverage patterns, the chip you are trying to locate will mostlikely be in the center of this pattern (assuming a matrix of course).

1. A system to identify gaming chips bet on a casino gaming table, thesystem comprising: a plurality of gaming chips each comprising an RFIDdevice which comprises a unique RFID number and a peripheral bar coderepresenting a denomination; a casino gaming table comprising playerbetting positions for betting one or more of the plurality of chips;means associated with at least one given position for reading opticalbar codes of any chip of the plurality of chips placed in the givenposition and providing the number thereof; means also associated withthe given position comprising two or more antennas for transmittinginterrogation signals in an excitation sequence to respective RFIDdevices of any chip of the plurality of chips placed in the givenposition and for receiving a signal sequence from the respective RFIDdevices in response to the interrogation sequence; and means forprocessing a received signal sequence to identify respective unique RFIDnumbers and providing the number thereof and for comparing the number ofchips provided by the means for processing and the number provided bythe means for reading optical bar codes.
 2. The system of claim 1,wherein the two or more antennas comprises at least one other antennawith different a coverage pattern than the two or more antennas.
 3. Thesystem of claim 2, wherein the one other antenna is positioned betweenthe two or more antennas.
 4. The system of claim 1, wherein the meansfor processing employs a computer algorithm to determine which antennasare excited and the excitation sequence thereof.
 5. The system of claim1, wherein the means for transmitting interrogation signals in anexcitation sequence does not provide for signals from every antennaassociated with the at least one given position.
 6. The system of claim5, wherein the means for processing employs a computer algorithm todetermine the excitation sequence for the antennas that transmitintegration signals.